1. Field of the Invention
The present invention relates to an in-wheel motor system for use in a vehicle having direct drive wheels as drive wheels.
2. Description of the Prior Art
It is generally known that, in a vehicle having a suspension mechanism such as a spring around a wheel, as the mass of parts under the spring such as a wheel, knuckle and suspension arm, so-called “unsprung mass” increases, changes in the ground holding force of a tire when running on an uneven road become larger, thereby deteriorating road holding properties.
In a vehicle driven by a motor such as an electric car, an in-wheel motor system incorporating a motor in a wheel is being employed. However, in a conventional in-wheel motor which is fixed to a spindle shaft connected to a part such as an upright or knuckle which is one of the parts around a wheel of the vehicle, the above unsprung mass increases by the weight of the in-wheel motor, whereby changes in the ground holding force of the tire become large, thereby deteriorating road holding properties (refer to patent documents 1 to 3, for example).
To solve the above problem, there is proposed an in-wheel motor system as shown in FIG. 4 in which a non-rotating side case 3a supporting a stator 3S elastically supported to a knuckle 5 by a buffer mechanism 50 having two plates 54 and 55 whose moving directions are limited to the vertical direction of the vehicle by direct-acting guides 51 and which are interconnected by springs 52 and a damper 53 moving in the vertical direction of the vehicle and a rotating side case 3b supporting a rotor 3R and a wheel 2 are interconnected by a flexible coupling 60 comprising a plurality of hollow disk-like plates 61A to 61C which are interconnected by direct-acting guides 62A and 62B arranged in such a manner that their moving directions are orthogonal to each other (refer to patent document 4, for example).
More specifically, as shown in FIG. 5, the above buffer mechanism 50 is connected to an axle 6 connected to the knuckle 5, four springs 52 which expand and contract in the vertical direction of the vehicle are installed in the four corners of a knuckle attachment plate 55 positioned on the suspension member 7 side, two dampers 53 which expand and contract in the vertical direction of the vehicle are mounted on both sides of a connection hole 55h for the axle 6 formed in the center of the knuckle attachment plate 55, spring receivers 52n are installed at positions corresponding to positions above or below the above springs 52 of a motor attachment plate 54 positioned on the motor 3 side, damper attachment portions 53n are mounted at positions corresponding to positions above the dampers 53, and the above plates 54 and 55 are interconnected by four direct-acting guides 51 which are arranged symmetrical to the center of the plates. Thereby, the motor attachment plate 54 and the knuckle attachment plate 55 are guided in the vertical direction of the vehicle by the above four direct-acting guides 51 and interconnected by the springs 52 and the dampers 53, thereby making it possible to limit the movement of the in-wheel motor 3 to the vertical direction while attenuation force is generated.
In the in-wheel motor system constituted as described above, the in-wheel motor 3 is float mounted to a part around the wheel so that the motor 3 itself can be used as the weight of a dynamic damper, thereby making it possible to improve ground holding performance and riding comfort when running on a bad road. Since the motor shaft and the wheel shaft are interconnected by the above flexible coupling 60 in such a manner that they can become eccentric to each other in any direction, torque can be transmitted from the motor 3 to the wheel 2 efficiently.
Patent document 1: Japanese Patent No. 2676025
Patent document 2: Japanese Examined Patent Publication No. 9-506236
Patent document 3: Japanese Unexamined Patent Application No. 10-305735
Patent document 4: WO 02/083446 A1